Phonon Scattering by Defects and Grain Boundaries at High Temperature in Polycrystalline Lanthanum Tellurides of Various Compositions

Abstract

During the past ten years, both theoretical and experimental work on the thermal conductivity of SiGe alloys has shown the importance of grain boundary scattering at high temperatures [1,2]. A grain size of less than 5 m reduced the lattice thermal conductivity by around 35% below the single crystal value at 1000K in heavily-doped alloys [3]. This decrease is believed to be due to the scattering of low-frequency (long wavelength) acoustic phonons by the grain boundaries. These phonons carry a large fraction of the heat in these alloys at high temperatures because the high-frequency (short wavelength) phonons are scattered by the Si-Ge mass difference.